Lagos , Nigeria -LRB- CNN -RRB- -- Nigeria 's ailing President Umaru Yar ` Adua , who gave amnesty to armed militants in the troubled oil-rich Niger Delta region , died Wednesday , the country 's information minister said . He was 58 .

Yar ` Adua had not been seen in public since November , when he went to Saudi Arabia for treatment of an inflammation of tissue around his heart . He was diagnosed with that condition , acute pericarditis , last fall after he complained of chest pain .

He returned to Nigeria in February but had remained out of sight .

Vice President Goodluck Jonathan has served as the country 's acting leader since Yar ` Adua fell ill .

Yar ` Adua took office in 2007 in an election mired in controversy and accusations of vote-rigging .

`` There was ballot snatching , voters were molested , voters were beaten ... and also payment inducement to vote for certain candidates , '' said Eneruvie Enakoko of the Civil Liberties Organization , a human rights group in Lagos .

The president , a soft-spoken and unassuming figure who did not bask in the media spotlight like past leaders of the West African nation , pledged to fight to improve the country of 150 million people despite the accusations .

`` Our collective goal is to deliver for our children a Nigeria better , stronger , more peaceful , more secure and more prosperous than we met it , '' Yar ` Adua said .

President Barack Obama issued a statement late Wednesday expressing his condolences to Yar ` Adua 's family and the Nigerian people .

`` President Yar ` Adua worked to promote peace and stability in Africa through his support of Nigerian peacekeeping efforts as well as his strong criticism of undemocratic actions in the region , '' Obama said in the statement . `` He was committed to creating lasting peace and prosperity within Nigeria 's own borders , and continuing that work will be an important part of honoring his legacy . ''

His election followed wide support from his predecessor , leading critics to label him a puppet of the former president , Olusegun Obasanjo .

After he was elected , Yar ` Adua replaced some of Obasanjo 's top officials , including the head of the army , a move analysts said was aimed at shedding off his predecessor 's influence .

One of Yar ` Adua 's biggest successes was offering amnesty to militants in the troubled oil-rich Niger Delta region , a move that brought fragile peace to the area after years of conflict . The well-armed Niger Delta rebels have been battling Nigeria 's armed forces over oil profits , which they say are unequally distributed .

While he has hospitalized in Saudi Arabia , the militants called off the truce , dealing a blow to plans to end violence that has crippled oil production in the nation .

Analysts say he did little to institutionalize reform in a country where two-thirds of the population lives on less than a dollar a day .

`` Because many people feel disillusioned economically and as long as they have those sentiments -- I think the risk of radical uprisings in places like northern Nigeria and certainly southern Nigeria in the Delta will continue regardless of who is in power , '' said Rolake Akinola , an analyst at Control Risks West Africa .

Yar ` Adua , a former chemistry teacher , was married twice and has nine children .

CNN 's Faith Karimi and Christian Purefoy contributed to this report .

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Nigeria 's information minister says President Umaru Yar ` Adua has died

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Yar ` Adua had given amnesty to armed militants in troubled oil-rich Niger Delta region

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He went to Saudi Arabia in November for heart treatment

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Yar ` Adua took office in 2007 in election mired in controversy , accusations of vote-rigging